According to Wikipedia:
"…Biblical references suggest that King David and the prophet Daniel prayed three times a day. In Psalms, David states: "Evening, morning and afternoon do I pray and cry, and He will hear my voice" (55:18). As in Daniel: "[...] his windows being open in his chamber toward Jerusalem, he kneeled upon his knees three times a day, and prayed, and gave thanks before his God, as he had done before" (6:11).
Orthodox Judaism regards halakha (Jewish law) as requiring Jewish men to pray three times daily and four times daily on the Sabbath and most Jewish holidays, and five times on Yom Kippur. Orthodox Jewish women are required to pray at least daily, with no specific time requirement…"